1. Technical Field
The present invention relates generally to high throughput screening of lubricating oil compositions for lubricant performance.
2. Description of the Related Art
The use of a combinatorial approach for materials synthesis is a relatively new area of research aimed at using rapid synthesis and screening methods to build libraries of polymeric, inorganic or solid state materials. For example, advances in reactor technology have empowered chemists and engineers to rapidly produce large libraries of discrete organic molecules in the pursuit of new drug discovery, which have led to the development of a growing branch of research called combinatorial chemistry. Combinatorial chemistry generally refers to methods and materials for creating collections of diverse materials or compounds—commonly known as libraries—and to techniques and instruments for evaluating or screening libraries for desirable properties.
Presently, research in the lubricant industry involves individually forming candidate lubricating oil compositions and then performing a macro-scale analysis of the candidate compositions by employing a large amount of the candidate to be tested. Additionally, the methods employed for testing each candidate composition require manual operation. This, in turn, significantly reduces the number of compositions that can be tested and identified as leading lubricating oil compositions.
Drawbacks associated with conventional screening procedures can be seen as follows. For example, governmental and automotive industry pressure towards reducing the phosphorous and sulfur content of lubricating oil compositions used as, for example, passenger car and heavy duty diesel engine oils, is leading to new research to identify oil compositions which can satisfy certain tests such as, for example, oxidation, wear and compatibility tests, while containing low levels of phosphorous and sulfur. In this context, United States Military Standards MIL-L-46152E and the ILSAC Standards defined by the Japanese and United States Automobile Industry Association at present require the phosphorous content of engine oils to be at or below 0.10 wt. % with future phosphorous content being proposed to even lower levels, e.g., 0.08 wt. % by June 2004 and below 0.05 wt. % by January 2006. Also, at present, there is no industry standard requirement for sulfur content in engine oils, but it has been proposed that the sulfur content be below 0.3 wt. % to meet June 2007 requirements for emissions. Thus, it would be desirable to decrease the amount of phosphorous and sulfur in lubricating oils still further, thereby meeting future industry standard proposed phosphorous and sulfur contents in the engine oil while still retaining the oxidation or corrosion inhibiting properties and antiwear properties of the higher phosphorous and sulfur content engine oils. In order to accomplish this, a large number of proposed lubricating oil compositions must be tested to determine which compositions may be useful.
Additionally, similar changes in specifications and changing customer needs also drive reformulation efforts in other lubricant applications such as, for example, transmission fluids, hydraulic fluids, gear oils, marine cylinder oils, compressor oils, refrigeration lubricants and the like.
However, as stated above, present research in the lubricant industry does not allow for reformulation to occur in an expeditious manner. As such, there exists a need in the art for a more efficient, economical and systematic approach for the preparation of lubricating oil compositions and screening of such compositions for information correlating to the actual useful properties of the compositions.
For example, it would be desirable to evaluate multiple lubricating oil compositions for dispersancy. Dispersants are added to lubricating oil compositions to keep engines clean by dispersing sludge, soot and varnish-forming deposits in the oil. Sludge can form in an internal combustion engine when, for example, combustion products such as, for example, water, metal particles produced by engine wear, and various partially oxidized hydrocarbon molecules, enter the lubricating oil by blowing past the piston rings. The sludge is a highly viscous composition which inhibits proper flow of the lubricating oil, thereby impairing its effectiveness. The problem can be partially alleviated by running an engine hot over an extended period of time by, for example, extended highway driving, to evaporate the water component of the sludge and loosen up the oil. This allows the filter to work more effectively to remove abrasive particulates which contribute to engine wear. However, with stop-and-go traffic or short trips in city driving, sludge has a tendency to build up. Hence, the importance of identifying and selecting the most effective additives to prevent such a build up. Dispersants also keep soot particles small by preventing agglomeration.
Another consideration is how the various additives in the lubricating oil interact. The presence of one additive may affect the performance of another. Accordingly, testing for any particular performance property is complicated by the fact that an additive cannot be tested in isolation. Rather, many different lubricating oil formulations with various additives and percentage compositions must be tested.
Accordingly, it would be desirable to rapidly prepare and test for dispersancy a plurality of sample candidate lubricating oil compositions automatically, preferably utilizing small amounts of each sample.